🐛(backend) add link to "Open" text in recording email

Added a hyperlink to the "Open" text in step 1 of the recording
notification email instructions. Previously, "Open" was plain text
and users could only access their recording via the button below.
Now the text itself is a clickable link, improving accessibility
for email clients that may not render the button properly.

Updated MJML source template and all 4 locale files (en, fr, de, nl).

src/mail/mjml/screen_recording.mjml

@@ -37,7 +37,7 @@
           <mj-text>
             <p>{% trans "To keep this recording permanently:" %}</p>
             <ol>
-              <li>{% blocktrans %}Click the "Open" button below {% endblocktrans %}</li>
+              <li>{% blocktrans %}Click the "<a href="{{link}}">Open</a>" link below {% endblocktrans %}</li>
               <li>{% blocktrans %}Use the "Download" button in the interface {% endblocktrans %}</li>
               <li>{% blocktrans %}Save the file to your preferred location{% endblocktrans %}</li>
             </ol>